In general, micelle is referred to as thermally stable and uniform spherical structure formed of amphiphilic low-molecular weight materials (for example, low-molecular weight materials having hydrophilic groups as well as hydrophobic groups). When a water insoluble drug is dissolved and introduced into a compound having such a micelle structure, the drug is present inside the micelle, and the micelle formed thereby is reactive to variations in temperature or pH in the body and thus can accomplish target-directed drug delivery. Therefore, such micelle type compounds have high applicability as carriers for drug delivery.
Korean Patent Application No. 2001-0035265 discloses a method for preparing micelles using polyethylene glycol and a biodegradable polymer. Both materials used in the above method are advantageous in that they have biodegradability and bioaffinity. However, because they are not sensitive to variations in a certain factor such as pH, they have difficulty in drug delivery to the desired site.
Meanwhile, pH in the human body ranges from 7.2 to 7.4. However, it is known that pH in the vicinity of abnormal cells such as cancer cells is a weak acidic pH ranging from 6.0 to 7.2. Accordingly, many attempts are made recently to accomplish drug delivery specific to cancer cells by developing a technical means for carrying out drug delivery at a pH of 7.2 or lower.
U.S. Pat. No. 6,103,865 discloses a polymer using a pH-sensitive compound, sulfonamide. The sulfonamide used in the prior art becomes insoluble at a pH of 7.4 or lower and is ionized at a pH of 7.4 or higher to show acidity. The above pH-sensitive compound shows pH-sensitivity opposite to a target of cancer cell. Therefore, a basic compound is needed for targeting cancer cells.
US Patent No. 2004/0071654 A1 discloses a method for preparing a poly(β-amino ester) compound showing basicity. The poly(β-amino ester) is a kind of poly(β-amino acid) and has an ester group and tertiary amine group in the backbone thereof, and thus shows advantageous ionization characteristics including a change in water solubility depending on pH values.